Molecular pathogenesis of mucosa-associated lymphoid tissue lymphoma

Ubiquitin hubs in oncogenic networks

Ubiquitin is an important regulator of diverse biological functions including cell cycle progression, apoptosis, cell proliferation, and DNA damage responses. Crucial proteins involved in the control of such diverse functions are modified by ubiquitin and are frequently altered during oncogenesis. Here, we define such proteins as key-nodes regulated by ubiquitin, discuss examples of their oncogenic aberrations, and indicate how pharmacologic manipulation of such molecular hubs might improve anticancer therapy.

Cytogenetic abnormalities in MALT lymphomas and their precursor lesions from different organs. A fluorescence in situ hybridization (FISH) study

AIMS

To analyse the possible activation of distinct molecular pathways in mucosa-associated lymphoid tissue (MALT) lymphoma, we determined the prevalence of trisomies 3, 12, 18 in MALT lymphomas from different organs, as well as the prevalence of translocations of the MALT1 gene in a subset of primary breast MALT lymphomas. We compared the numerical cytogenetic alterations in lymphomas, precursor lesions and in normal non-haematolymphoid tissue from the same organs.

METHODS AND RESULTS

Forty-two samples of paraffin-embedded tissue (29 MALT lymphomas from stomach, breast, parotid and thyroid; two Sjögren's syndrome; two Hashimoto's thyroiditis and nine reactive samples) were studied by fluorescence in situ hybridization (FISH). Analysed together, the cases of gastric, parotid and thyroid MALT lymphomas presented trisomy 3 in 46%, trisomy 12 in 28% and trisomy 18 in 21% of the cases. In contrast to other locations, trisomy 3 was not present in the majority of the cases of primary breast MALT lymphomas. None of the nine breast cases presented MALT1 gene rearrangements. Half of the cases of preneoplastic lesions exhibited trisomy 3 and trisomy 12; none exhibited trisomy 18.

CONCLUSIONS

Trisomy 3 is the most frequent numerical abnormality in gastric, parotid and thyroid but not in primary breast MALT lymphomas. MALT1 gene rearrangements are also rare in this location, suggesting that distinct molecular pathways may be activated in breast cases.

MALT1, BCL10 and FOXP1 in salivary gland mucosa-associated lymphoid tissue lymphomas

In view of the certain anatomic site-dependent frequency of chromosomal translocations involved in extranodal marginal zone B cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) pathogenesis, 17 salivary gland MALT lymphoma cases were analyzed for MALT1 and FOXP1 translocations. B cell CLL/lymphoma 10 (BCL10) and forkhead box PA (FOXP1) protein expression were studied by immunohistochemistry and translocations identified using fluorescence in situ hybridization (FISH)-specific probes FOXP1, t(11;18)(q21;q21)/API2-MALT1 and t(14;18)(q32;q21)/IgH-MALT1. None of the 11 analyzed cases showed FOXP1 rearrangement or amplification. The t(11;18) was present in five of 13 cases and the t(14;18) in three of 13 cases. MALT1 translocations were mostly mutually exclusive except in a single case. FOXP1 protein expression showed differences in the proportion of tumor cells with nuclear expression but not in their intensity, with the exception of one case where very intense nuclear staining was noted. BCL10 nuclear expression was present in four of 17 cases, two of which lacked t(11;18). Our results suggest that MALT1-specific translocations and FOXP1 rearrangements are not commonly involved in pathogenesis. A case with strong FOXP1 protein expression indicates the possibility that the upregulation of FOXP1 expression is significant in a small subset of salivary gland MALT lymphomas. Also a single case in which both MALT1 translocations were present indicates that these are not always mutually exclusive.

Chromosome instability and translocation t(11;18) in primary gastric marginal zone B-cell lymphoma of MALT-type

The prognosis for patients with mucosa-associated lymphoid tissue (MALT) lymphomas is good; these tumours have usually an indolent course with overall survival rates that are greater than 80% at 5-year, but some rare cases with histological transformation in aggressive diffuse large cell lymphoma have also been diagnosed. Here, we present cytogenetic results on endoscopic bioptic material of 42 cases of primary gastric extranodal marginal zone B-cell lymphoma (EMZL) using fluorescence in situ hybridization (FISH) approach with API2, MALT1 and centromeric probes for chromosome 3 and 18, and their impact on the clinical outcome.

Antigen-receptor signaling to nuclear factor kappa B

Signal transduction events leading to the survival, differentiation, or apoptosis of cells of the innate or adaptive immune system must be properly coordinated to ensure the normal mounting and termination of immune responses. One of the key transcription factors in immune responses is nuclear factor kappaB (NF-kappaB), which has been the focus of intense investigation over the past two decades. With the identification of the CARMA1-BCL10-MALT1 complex and ongoing progress in understanding the molecular mechanisms connecting T cell and B cell receptor proximal signals to the IkappaB kinase (IKK) complex, a cohesive model of antigen receptor (AgR)-dependent signaling to NF-kappaB activation is beginning to emerge. In this review, we provide an overview of the current state of research into the mechanisms that regulate AgR-mediated NF-kappaB transcriptional activity, with particular focus on the events leading to activation of the IKK complex.

Chlamydia psittaci in ocular adnexal lymphoma: Japanese experience

We searched for the Chlamydia psittaci DNA the touchdown enzyme time release PCR (TETR-PCR) in 23 specimens from 21 patients with ocular adnexal lymphoproliferative disorders, including 12 patients with MALT lymphoma to identify C. psittaci infection. Southern hybridization of the PCR product using the C. psittaci-specific probe failed to detect C. psittaci, although three samples appeared to be positive by ethidium bromide staining. This indicates that technical approach for detecting C. psittaci infection in ocular adnexal lymphoma might be an essential in disclosing this association.

Primary cutaneous marginal zone B-cell lymphoma of MALT type in a child

Marginal zone B-cell lymphoma (MZBCL) of mucosa-associated lymphoid tissue type is a peculiar variant of B-cell neoplasm showing distinct clinical and pathologic features. Its occurrence in children or adolescents is extremely uncommon. We describe the case of an 11-year-old boy who developed such a lymphomatous process involving primarily the skin. The tumor was characterized by a maturing plasma cell population that included immunoblasts, heavy-chain but not light-chain restriction suggestive of monoclonality, and a prevalent, focally granulomatous component of histiocytes. As an additional interesting feature, a trisomy 3 was demonstrated by fluorescence in situ hybridization analysis. The clinical, morphological, phenotypic, and genetic characteristics seen in our patient do not differ significantly from those described in primary cutaneous MZBCL occurring in adults.

Integrin signals, transcription factors, and monocyte differentiation

The precise signals responsible for differentiation of circulating monocytes into tissue macrophages are incompletely defined. "Outside-in" integrin signaling has been implicated in modulating gene expression that affects cellular differentiation. This review highlights the role of transcription factors in monocyte differentiation and describes how integrin engagement orchestrates monocyte differentiation signals by regulating the expression of the forkhead transcription factor Foxp1, which functions as a transcriptional repressor of the macrophage colony-stimulating factor receptor c-fms. This represents a new pathway for integrin-dependent modulation of gene expression and control of cellular differentiation.

Lymphome pulmonaire du MALT révélant un sida

INTRODUCTION

We report the case of a patient with an isolated pulmonary mucosa associated lymphoid tissue (MALT) lymphoma that revealed an acquired immune deficiency syndrome (AIDS).

CASE REPORT

A 30 year old man from Central Africa was admitted to hospital with cough, dyspnoea and general weakness. A diagnosis of HIV infection was made promptly. The thoracic CT scan revealed diffuse bilateral ground glass opacities as well as consolidation of the right upper lobe. After a non-diagnostic endoscopy the diagnosis of a low grade B cell MALT lymphoma (CD20+) was made by lung biopsy and confirmed by the presence of the t(11;18) translocation. No extrathoracic lymphoma was found. Treatment with rituximab and triple anti-retroviral therapy led to a rapid and complete remission that was maintained for 3 years after the diagnosis.

CONCLUSION

Pulmonary MALT lymphoma may reveal AIDS. A combination of rituximab and anti-retroviral therapy led to complete remission in this patient.

High BCL6 expression predicts better prognosis, independent of BCL6 translocation status, translocation partner, or BCL6-deregulating mutations, in gastric lymphoma

To investigate the role of BCL6 in the pathogenesis of gastric lymphoma, we analyzed the BCL6 promoter region for BCL6 translocations, somatic hypermutations, and deregulating mutations in 43 gastric lymphomas, including 4 extranodal marginal-zone B-cell lymphomas of mucosa-associated lymphoid tissues (MALT lymphomas), 33 diffuse large B-cell lymphomas (DLBCLs), and 6 composite DLBCLs with residual MALT lymphoma (DLCLMLs). BCL6 promoter substitutions by immunoglobulin (Ig) and non-Ig translocation partners, resulting in its deregulation, were frequently involved in DLBCL (36.4%) and DLCLML (50%). Two novel BCL6 translocation partner genes, 28S rRNA and DMRT1, and a new BCL6 translocation breakpoint in intron 2 were also identified. Deregulating mutations were found only in DLBCL (24.2%), which correlated significantly with high BCL6 protein expression. Significantly, high BCL6 expression correlated strongly with longer overall survival (OS), independent of mechanism in gastric DLBCL and DLCLML. Gastric DLBCLs were further subclassified into germinal center B-cell-like (GCB) and non-GCB subgroups immunohistochemically. High BCL6 expression was detected in all GCB cases, irrespective of BCL6 genetic alterations. In the non-GCB subgroup, BCL6-deregulating mutations correlated significantly with high BCL6 expression level. No significant correlation was found between the BCL6 expression level and OS in the non-GCB subgroup, which had significantly poorer prognosis than the GCB subgroup.

Treatment of gastric mucosa-associated lymphoid tissue lymphoma: Helicobacter pylori eradication and beyond

Gastric mucosa-associated lymphoid tissue (MALT) lymphoma is the paradigm of lymphomas developing in extranodal areas after antigen stimulation. In the stomach, Helicobacter pylori colonization induces the appearance of MALT and, eventually, MALT-derived lymphoma. This type of lymphoma is initially a localized form of disease, but may disseminate and transform into high-grade lymphoma, making full staging (as for nodal lymphomas) and endoscopic ultrasonography to evaluate the penetration of the lymphoma through the gastric wall mandatory. In localized gastric MALT lymphoma, the first step in treatment is eradication of H. pylori, which results in 60-90% regression. This response is maintained for years in most patients, with only 10-15% relapse, frequently precipitated by H. pylori reinfection. A component of high-grade lymphoma, penetration to gastric serosa or beyond and translocation t(11;18) are the main factors that make lymphoma resistant to eradication. Surgery or radiotherapy can cure localized lymphomas in 75-90% of patients. Chemotherapy with alkylating agents, combination chemotherapy and purine analogs, and anti-CD20 antibodies can also induce remission of localized lymphomas refractory to eradication, as well as locally advanced and disseminated lymphomas. The optimum chemotherapy treatment for advanced disease has not yet been established; however, combination therapy, including purine analogs with or without anti-CD20, may be a promising option. Despite histological responses and prolonged remissions, residual molecular disease can be demonstrated in most cases treated with H. pylori eradication, radiotherapy or alkylating agents, and even after more intense chemotherapy, although this does not seem to lead to late relapses. High-grade gastric MALT lymphoma should be treated with chemotherapy, with cyclophosphamide, doxorubicin, oncovin and prednisone being the best first-line option. All gastric MALT lymphomas associated with H. pylori should receive eradication treatment in addition to other required treatment.

Specific peptides for the therapeutic targeting of oncogenes

Tumors are dependent on oncogenic proteins for their maintenance and survival. The ideal cancer therapy would include drugs that specifically target these proteins. Many such proteins function through interfaces that can be difficult to target effectively with small molecules. However, recent advances in cell-permeable peptide technology, improving cellular penetration and stability, raise the possibility that specific peptide interference of oncogenic proteins could be successfully translated to the clinic. Several active anti-tumor peptides were recently described. For example, a stable peptide inhibitor of the Hsp90 ATP-binding pocket killed a wide range of tumors in vitro and in vivo, and a peptide inhibitor of the BCL6 oncoprotein was active in B-cell lymphomas; both peptides functioned without toxicity to normal tissues.

Delving deeper into MALT lymphoma biology

Mucosa-associated lymphoid tissue (MALT) lymphomas can arise in a variety of extranodal sites. Interestingly, at least 3 different, apparently site-specific, chromosomal translocations, all affecting the NF-kappaB pathway, have been implicated in the development and progression of MALT lymphoma. The most common is the translocation t(11;18)(q21;q21), which results in a fusion of the cIAP2 region on chromosome 11q21 with the MALT1 gene on chromosome 18q21 and is present in more than one-third of cases. The frequency of this translocation is site-related: common in the gastrointestinal tract and lung, rare in conjunctiva and orbit, and almost absent in salivary glands, thyroid, liver, and skin. In this issue of the JCI, Hu et al. add to our understanding of the molecular consequences of this translocation, showing that its fusion product, cIAP2-MALT1, may concomitantly contribute to lymphomagenesis both as a tumor suppressor gene and as an oncogene.

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